Digital electronic micrometer

Abstract

A digital electronic micrometer eliminates backlash and other error between a movable probe and a digital readout and arranges all the working components within a handle thermally insulated from the probe and the yoke. An optical scale is secured to the probe to move directly with the probe past an electro-optical reader arranged within the tool handle, and a manually operable retractor moves the probe away from the anvil against the bias of a spring. Electronic circuitry and digital display can also be arranged in the tool handle for indicating positions of the probe relative to the frame, and the circuitry includes manually actuatable hold circuitry for maintaining the display at an indication of a previous position of the probe after movement of the probe. This allows the tool to be moved to an orientation for observing a measurement previously taken when the tool was in a position obscuring the reading. The circuitry also preferably includes error detection circuitry responsive to change of state of a signal from the reader at more than a predetermined rate or to movement of the probe during actuation of the hold circuitry for energizing an error indicator.

We claim: 
     
       1. A digital electronic micrometer having a frame including a yoke, an anvil on said yoke, and a bushing, a probe supported by said bushing and movable relative to said anvil, and a spring for biasing said probe toward said anvil, said micrometer comprising: a. a handle secured to said frame and configured to be held in one hand for manually holding and operating said micrometer without touching said yoke;   b. said handle being hollow and enclosing parts of said micrometer;   c. said handle being formed of a resin material for thermally insulating the heat of said hand holding said handle from said yoke and said frame;   d. an optical scale secured to said probe to extend in the direction of motion of said probe and move directly with said probe within said handle;   e. a reader assembly fixed relative to said direction of motion of said probe and arranged within said handle so that said scale is movable relative to said reader assembly and movement of said scale is electro-optically detected by said reader assembly;   f. a retractor secured to said probe and having a portion external of said handle and operable by said hand holding said handle for manually moving said probe away from said anvil against the bias of said spring;   g. electronic circuitry and a digital display cooperatively responsive to said reader assembly for indicating positions of said probe relative to said frame;   h. said electronic circuitry including manually actuatable hold circuitry for maintaining said display at an indication of a previous position of said probe after movement of said probe from said previous position; and   i. a switch arranged on said handle to be manually accessible by said hand holding said handle for actuating said hold circuitry.   
     
     
       2. The micrometer of claim 1 wherein said electronic circuitry and said digital display are arranged within said handle. 
     
     
       3. The micrometer of claim 1 wherein said external portion of said retractor is manually slidable along said handle in said direction of motion of said probe. 
     
     
       4. The micrometer of claim 3 wherein said retractor is formed of resin material and has a flexible region between said probe and said external portion to allow flexing of said external portion and to limit stress on said probe from movement of said external portion. 
     
     
       5. The micrometer of claim 1 wherein said spring is helical and arranged within said handle, a pulley is arranged within said handle to move with said probe and said scale, a tension strand extends from said spring around said pulley, and the free end of said tension strand is fixed relative to said frame. 
     
     
       6. The micrometer of claim 1 wherein a beam is mounted on said frame within said handle to extend parallel with said direction of motion of said probe, and said reader assembly is mounted on said beam. 
     
     
       7. The micrometer of claim 6 wherein said retractor has a portion straddling said beam for guiding said retractor along said beam. 
     
     
       8. The micrometer of claim 7 wherein said external portion of said retractor is manually slidable along said handle in said direction of motion of said probe and said retractor is formed of resin material and has a flexible region between said probe and said external portion to allow flexing of said external portion and to limit stress on said probe from movement of said external portion. 
     
     
       9. The micrometer of claim 6 wherein said spring is helical and arranged within said handle, a pulley is arranged within said handle to move with said probe and said scale, a tension strand extends from said spring around said pulley, and the free end of said tension strand is fixed relative to said frame. 
     
     
       10. The micrometer of claim 6 wherein said electronic circuitry and said digital display are arranged within said handle. 
     
     
       11. The micrometer of claim 1 including an error indicator and wherein said electronic circuitry includes error detection circuitry responsive to change of state of a signal from said reader at more than a predetermined rate for energizing said error indicator. 
     
     
       12. The micrometer of claim 11 wherein said error detection circuitry is also responsive to movement of said probe from said previous position during actuation of said hold circuitry for energizing said error indicator. 
     
     
       13. The micrometer of claim 12 wherein said electronic circuitry, said digital display, and said error indicator are arranged within said handle. 
     
     
       14. The micrometer of claim 12 wherein said external portion of said retractor is manually slidable along said handle in said direction of motion of said probe and said retractor is formed of resin material and has a flexible region between said probe and said external portion to allow flexing of said external portion and to limit stress on said probe from movement of said external portion. 
     
     
       15. The micrometer of claim 1 including an error indicator and wherein said electronic circuitry includes error detection circuitry responsive to movement of said probe from said previous position during actuation of said hold circuitry for energizing said error indicator. 
     
     
       16. The micrometer of claim 15 wherein said electronic circuitry, said digital display, and said error indicator are arranged within said handle. 
     
     
       17. The micrometer of claim 16 wherein said external portion of said retractor is manually slidable along said handle in said direction of motion of said probe and said retractor is formed of resin material and has a flexible region between said probe and said external portion to allow flexing of said external portion and to limit stress on said probe from movement of said external portion.